1. Field of the Invention
This invention relates to a swash plate compressor.
2. Description of the Prior Art
In general, a swash plate compressor includes a swash plate which is fitted on a drive shaft, for rotation in unison with the drive shaft, and a plurality of pistons each of which is connected to the swash plate via a pair of generally hemispherical shoes sliding on front and rear sliding surfaces of the swash plate, respectively, for reciprocation within a cylinder bore according to the rotation of the swash plate.
Each of the pistons is comprised of a body formed with a first concave portion for slidably supporting one of the shoes, a front end portion formed with a second concave portion for slidably supporting the other of the shoes, and a bridge integrally formed with the body and the front end portion for connecting the two portions to each other.
The first and second concave portions are opposed to each other axially, i.e. in a direction of reciprocation of the piston with space therebetween.
The pair of shoes are arranged on opposite outer peripheral portions of the swash plate such that they are opposed to each other via the swash plate to form an imaginary sphere.
As the swash plate rotates, each piston reciprocates within a corresponding one of the cylinder bores, whereby refrigerant gas within the cylinder bore is compressed.
In a swash plate compressor for use in a typical refrigeration cycle system using a chlorofluorocarbon as a refrigerant, an imaginary sphere formed by a pair of shoes has a diameter which is approximately half as large as an outer diameter of each piston.
On the other hand, in a swash plate compressor for a transcritical refrigeration cycle system using carbon dioxide (CO.sub.2) as a refrigerant, delivery quantity or capacity of the compressor is approximately a sixth of that of the compressor using the chlorofluorocarbon, due to differences in property between the two refrigerants. Therefore, each piston of the compressor using CO.sub.2 has an outer diameter smaller than that of the piston of the compressor using chlorofluorocarbon. More specifically, the former may be less than half of the latter.
However, since the transcritical refrigeration cycle is a high-pressure cycle in which load applied to shoes by compression pressure during each compression stroke is no lower than when the chlorofluorocarbon is compressed, it is required that the imaginary sphere formed by the pair of shoes has a diameter which is substantially equal to or slightly larger than the outer diameter of the piston, in view of rigidity of the shoes and slidability between the shoes and the swash plate.
Therefore, if the conventional construction of the piston (in which the bridge and the front end portion do not extend radially outward with respect to the peripheral surface of the body) is employed, it is inevitably required to reduce the shoes in size, which makes it impossible to obtain the required rigidity and slidability of the shoes.